Hydrogeochemical investigation of an epithermal mineralization bearing basin using multivariate statistical techniques and isotopic evidence of groundwater: Kestanelik Sub-Basin, Lapseki, Turkey

Abstract

This study investigates hydrogeochemical processes controlling the groundwater quality using 64 groundwater samples in the epithermal mineralization bearing Kestanelik Sub Basin, NW Turkey. The groundwater dominantly exhibits a mixed-ion hydrochemical facies characterized by Ca-Mg-HCO3, Mg-Ca-HCO3, Ca-Mg--HCO3-SO4 and Ca-Mg-Na-HCO3 reflecting weakly mineralized waters circulating within calcareous sandstone and colluvium. The molar ratios of (Ca2++Mg2+)/(SO42-+HCO3-) and Na+/Cl-ratios and the linear plot between (Na++K+)-Cl- and (Ca2++Mg2+)-(HCO3-+SO42-) indicate that of dissolution of carbonates and silicate weathering, ion and reverse ion exchange processes influence the hydrogeochemistry of groundwater sources. Three and four factors account with 84.48 and 75.27 % of the total variance for spring and well waters, respectively. FC1 in the groundwater samples is described by strong loadings of TH, Ca2+, Mg2+, HCO3-, Ba, TDS, Cl-, EC and SO42-, and moderate loading of Na+, Mn, K+, TDS, pH. FC2 in the samples has strong positive loadings on Al, Fe, Zn, Na+, SO42-, Cl- and moderate positive loadings on B, TDS and K+. FC3 shows strong positive loading on Cu, Al, DO and moderate factor loadings for Fe in the well water samples. FC4 exhibits high positive loadings for As, Zn, and moderate positive loading for EC. Geochemical variables of FC 1, 2, 3 and 4 for the groundwater indicates mixed geogenic source of groundwater contamination through water-rock interaction processes dominantly from (i) the calcareous sandstone, serpentinite and colluvium lithologies and (ii) quartz, illite, pyrite and iron oxide minerals sourced from epithermal mineralization in the area. pH and As values exceed the desirable limits of WHO and TSE 266 guidelines for drinking purpose. The tritium levels show that some well waters have experienced longer water-rock interaction and residence time and are thus recharged from older groundwater sources compared to other well and spring waters.